Fluid-operated, torque transfer devices used as drive ratio establishing devices, such as clutches and brakes, in vehicular transmissions frequently utilize a pressure-operated piston that is slidably disposed within a chamber. Such pistons are generally provided with one or more annular seals that cooperate with the annular walls of the chamber to prevent leakage of hydraulic fluid therebetween when the torque transfer device is pressurized--i.e.: during engagement of the torque transfer device to select a specific drive ratio. Generally, the seals are either "O" rings or "square" rings which are fitted in a groove provided in the piston in a manner such that the walls of the cylinder will be physically engaged thereby to seal the chamber.
Other torque transfer or similar devices use a bonded piston and seal assembly--such as that shown in U.S. Pat. No. 4,635,778 issued Jan. 13, 1987, to Lederman and assigned to the assignee of the present invention--to provide an assembly that is more easily manipulated in production. These assemblies typically have a rigid core, generally made of steel, to which an elastomeric member is bonded. These assemblies have been found very useful in the manufacture of vehicular transmissions. Other known bonded piston and seal assemblies have an outer periphery comprised of two annular nodes which provide a piston support rib and a transition rib. At least one, and usually both, of the nodes is aligned transversely with respect to the axis of the rigid core.
The prior art piston and bonded seal assemblies often exhibit a drawback when the transmission is subjected to extensive temperature fluctuations. For example, if the temperature ranges from a low of at least minus thirty degrees Fahrenheit (-30.degree. F.) to a high of more than about three hundred degrees (300.degree. F.), the seal material disposed about the rigid core is severely stressed and can become detached from the core at or near the intersection of an annular wall with a radially wall of the seal. This separation will generally occur on the pressure side of the piston.